Most surprising, the researchers found the damage occurred if the liquid did not contain nicotine. "We have provided strong evidence that the liquid used in e-cigarettes, whether it contains nicotine or not, has negative effects on the airways and on the lungs," Dr. Chu says.

It's important to note that the study was done on cells in a dish, not on people. But those cells that line the airways, called epithelial cells, are the first line of defense against any virus we may inhale.

The takeaway from this and other studies on electronic cigarettes seems to be: If you are not using nicotine now, don't assume this is a safe way to start.